EntityFramework 学习 一 Lazy Loading 1

延迟加载：延迟加载相关的数据

using (var ctx = new SchoolDBEntities())
    {
        //Loading students only
        IList<Student> studList = ctx.Students.ToList<Student>();

        Student std = studList[0];

        //Loads Student address for particular Student only (seperate SQL query)
        StudentAddress add = std.StudentAddress;
    }
    

首先查询Student表

SELECT 
[Extent1].[StudentID] AS [StudentID], 
[Extent1].[StudentName] AS [StudentName], 
[Extent1].[StandardId] AS [StandardId]
FROM [dbo].[Student] AS [Extent1]
        

再查询StudentAddress表

exec sp_executesql N'SELECT 
[Extent1].[StudentID] AS [StudentID], 
[Extent1].[Address1] AS [Address1], 
[Extent1].[Address2] AS [Address2], 
[Extent1].[City] AS [City], 
[Extent1].[State] AS [State]
FROM [dbo].[StudentAddress] AS [Extent1]
WHERE [Extent1].[StudentID] = @EntityKeyValue1',N'@EntityKeyValue1 int',@EntityKeyValue1=1

可以为指定的属性或整个上下文关闭延迟加载的功能，关闭属性的延迟加载功能就是不要设置属性为virtual

using System;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Data.Entity.Core.Objects;
using System.Linq;
    
public partial class SchoolDBEntities : DbContext
{
    public SchoolDBEntities(): base("name=SchoolDBEntities")
    {
        this.Configuration.LazyLoadingEnabled = false;
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        throw new UnintentionalCodeFirstException();
    }
}
  

 延迟加载的规则：

1.context.Configuration.ProxyCreationEnabled必须为true

2.context.Configuration.LazyLoadingEnabled必须为true

3.导航属性必须定义为public virtual